Add support for edge_project to QueryBuilder constructor

[sphuber]

This functionality is currently only accessible through the QueryBuilder.append method. However, the REST API uses the method of initialization through the constructor

[sphuber]

Apparently, this is already supported but not documented and the syntax is weird.

query_help = {
    'path': [{
        'cls': orm.Node,
        'tag': 'n1',
    }, {
        'cls': orm.Node,
        'tag': 'n2',
        'edge_tag': 'n1--n2',
        'with_incoming': 'n1'
    }],
    'filters': {
    },
    'project': {
        'n1': ['id', 'uuid', 'ctime'],
        'n2': ['id', 'description'],
        'n1--n2': [{'label': {}}, {'type': {}}]
    },
} 

Note that for the edge projections on edge n1--n2 one does not have to specify a flat list but a list of dictionaries where the key is the desired projection and its value is always an empty dictionary.